Abstract In the United States, 20% of children live in food insecure or marginally secure conditions, defined by limited or uncertain access to food (1, 2). Even at the lowest levels of severity, food insecurity is paradoxically associated with increased body mass index (BMI) (3) and populations that experience food insecurity are at greater risk for substance abuse issues (4-8). Further progress in delineating the role of food insecurity on substance use and obesity in humans is handicapped by co-occurrence of other aspects of adversity such as neglect, abuse and maternal mental illness. Here we propose to further develop our mouse model of food insecurity in which meals are delivered to mice in an irregular pattern for a brief developmental window. We compare these mice to stably food restricted and ad libitum fed controls. Because dopamine neurons fire phasically in response to unpredicted events (reward prediction error), we hypothesize that uncertainty may be an important variable independent from scarcity. We posit that cumulative experience of unpredictable food delivery will alter maturation of dopamine neurons and downstream circuits, altering reward and decision- making behavior. Our initial experiments show that adult male mice that experienced food insecurity P21-40 are less flexible in a reversal task compared to mice that experienced a history of regular food restriction or ad libitum fed controls. Females show no effect of treatment on flexibility in reversal but a treatment related increase in adult ad lib weight. Here we propose to test if there is a sensitive period for exposure to food insecurity by moving exposure to different ages (Aim 1) and to evaluate the impact of treatment at different ages on adult reward integration (Aim 1). We will also use pre-pubertal ovariectomy to test the role of pubertal hormones in the observed sex difference (Aim 1). We will next (Aim 2) determine if food insecurity enhances vulnerability in the context of substance use by measuring ethanol consumption in an intermittent access two bottle choice paradigm (which can elicit binge drinking) and aversion resistant ethanol consumption in which the only available ethanol is adulterated with quinine (a model of compulsive drinking). Here we will also test both sexes to investigate sex differences. We will also investigate if inflexibility in a cognitive test of reversal will predict later insensitivity to quinine adulteration of ethanol. Our major goals for the end of the grant period are: 1) To have established when it matters most to the developing brain to experience food insecurity, a question highly relevant to policy and public health. 2) To have tested the hypothesis that early food insecurity predisposes individuals to show greater binge or compulsive substance use in the context of ethanol, a causal link that is impossible to isolate without large confounds in humans. A future R01 will investigate neurobiological changes in the dopaminergic system and its cortical-striatal targets that may mediate observed changes in behavior.